Transformer coupled flip-flop



April 12, 1960 w. N. CARROLL 2,932,795

TRANSFORMER COUPLED FLIP-FLOP Filed April 29, 1955 I 1.5mh 33 34INVENTOR. WILLIAM N.CARROLL w v /gm ATTORNEY 2,932,795 I TRANSFORMERCOUPLED FLIP-FLU William N. Carroll, Wappingers Falls, N.Y., assignor toInternational Business Machines Corporation, New York, N .Y., acorporation of New York Application April 29,1955, Serial No. 504,868 3Claims. (Cl. 328-496} The present invention relates to an electroniccircuit and more particularly to an electronic circuit of the flipiiopor trigger type.

An object of the present invention is to provide an improved electronicswitching circuit of the dual tube type including transformer couplingbetween the anodes of the respective tubes.

Another object of the present invention is to provide an improvedtrigger circuit adapted to decrease the transition time from one stablestate to the other and thereby decrease the rise or fall time of theoutput waveform during each transition.

A further object of the present invention is to provide an improvedflip-flop circuit wherein the transformer coupling between the anodes ofthe trigger tubes aids transition by maintaining the formerly conductingtube in a cutoff condition until completion of transition.

Other objects of the invention will be pointed out in the followingdescription and claims and illustrated in the accompanying drawings,which disclose, by way of example, the principle of the invention andthe best mode, which has been contemplated, of applying that principle.

In the drawings:

Fig. 1 is a schematic diagram of a ment of the present invention.

Fig. 2 illustrates a family of waveforms identifying the negative signalappearing at the secondary of the input transformer and the Waveform ofthe output signal with and without transformer coupling.

Referring now to the drawings and more particularly to Fig. 1 thereof,there is illustrated in block and schematic form a preferred embodimentof the present invention. As is well known in the art, a flip-flop is abi-stable switclun device which operates so that it is always in one oftwo stable conditions, the switching from one stable condition to theother being generally accomplished by the application of a shortduration pulse applied to the input or inputs of the flip-flop circuit.

As shown in block form in Fig. 1, the subject flip-flop i has two inputsand a corresponding number of outputs. A positive pulse applied to theSet input terminal 2 produces a positive DC. level at the left outputlabeled conductor 4, and a negative D.C. level at the right outputlabeled conductor a positive pulse applied to the Clear input terminal 3produces a negative D.C. level output on conductor 4 and a positive D.C.level on conductor 5. In the ensuing description, the above describedformet and latter conditions are referred to as the On and Off conditionrespectively.

Referring now to the schematic diagram of Fig. 1, flipflop l is asymmetrical circuit comprising two substantiaily indentical circuits,each of these circuits including a trigger tube and associatedcircuitry. With respect to the ensuing description, it is assumed thatthe flip-flop circuit is initially in the Off condition, i.e., triggertubes 21 and 22, which may be the respective halves of a Z 2l7'7 twintriode, for example, are in the conducting and non-conducting statesrespectively. Anodes 23 and preferred embodiice 24 are cross coupled tocontrol grids 25 and 26, while cathodes 27 and 23 are connected througha common resistor 29 to a source of negative potential at terminal 3d.Resistor 29 provides cathode degeneration for trigger tubes 21 and 22.Operating DC. potential is supplied from terminal 31 to anodes 23 and 24through peaking coils 33 and 34 and transformer windings 35 and 35respectively. Peaking coils 33 and 34 are tapped from voltage dividernetworks comprising resistors 41, 42 and 53, 44, each of such networksbeing serially connected between a source of volts potential and ground.

A further voltage divider network constituting part of the load circuitfor anode 23 includes resistors 45 and do serially connected betweenanode 23' and a source of -300 volts potential at terminal 3%. Anidentical network comprising resistors 48, 49, and connected betweenanode 24 and terminal 30, functions as part of the load circuit foranode 24. Control potential for grid 26 of trigger tube 21 is obtainedfrom the junction of resistors id and 39 through parasitic suppressor5i. Capacitor 52, connected across coupling resistor 43, serves as acompensating capacitor and also functions to decrease the transitiontime required to switch from one conduction state to the other byensuring that the signal couple from anode 24 of trigger tube 22 tocontrol grid 26 of trigger tube 21 during a transition of state isapplied with sufticient amplitude and proper shape to ensure transition.Since the capacitance of condenser 52 is appreciably higher than thecapacitance of trigger tube 21, control grid 26 of trigger tube 21 isforced to respond more rapidly to the change in anode potential oftrigger tube 22. Thus any change of potential on anode 2d of triggertube 22 results in a nearly instantaneous change in potential on controlgrid 26. Furthermore, with capacitor 52 shunting resistor -48,substantially the full anode swing appears on control grid 26 sinceresistor 43 is effectively short circuited for these short periodchanges. Capacitor 52 also functions as a memory capacitor to insurethat'trigger tube 21 is rendered conductive whenever tubes 21 and 22 aremomentarily rendered non-conductive during the transition from the Offto the On state, i.e., vacuum tube 21 is rendered con ductive afterpreviously being non-conductive. Similarly, control voltage for grid 25of trigger tube .22 is obtained from the junction of resistors 45 and 46through parasitic suppressor 53, while capacitor 54, connected acrosscoupling resistor 45, serves as a compensating and memory capacitorassociated With trigger tube 21. Diodes 51-, 58 and 59, 6d, connected topotential sources of -30 and +10 volts respectively, function to controlthe lower and upper levels of the output signal, and further define theanode potentials of the conducting and non-conducting trigger tubesrespectively.

in order to facilitate an understanding of the present invention, theoperation of the subject apparatus will be described in detail withreference to Fig. 1. In the ensuing description, it is again assumedthat the flip-flop is initially in the OE condition.

When a positive pulse of 20-49 volts in amplitude is ,pplied to the Setinput terminal 2, a negative pulse of .l ,lLSeC. is produced intransformer secondary winding When trigger tube 21 is conducting, itsgrid bias is tp roximately Zero with respect to the cathode, while tscutoff bias is in the order of 8 volts. Since diode is positioned in aloop between grid and cathode, it similarly biased and therefore is atthe threshold of onduction. One end of transformer secondary winding 3is connected directly to a common terminal 64 of athodes 2'7 and 23,while the other end is connected to the cathode of diode 65. Thecombination of diode 67 and resistor 68 connected across secondarywinding 63 is a damping network to prevent transformer 62, from 3ringing or oscillating, and further serves to limit positive overshootvoltages which occur on the upper side of secondary winding 63 as aresult of the decay of the initiating positive pulse.

The negative pulse produced in the transformer secondary winding 63causes the cathode of diode 65 to go further negative with respect toits anode, whereupon diode 65 conducts and the negative signal passesthrough parasitic suppressor 51 to control grid 26 of trigger tube 21.Substantially the full negative pulse is passed by diode 65, providedthat the potential on its anode is zero or positive relative to thepotential on its cathode. The applied pulse as heretofore described isof sufficient amplitude to cause trigger tube 21 to cut off, which inturn causes trigger tube 22 to conduct in a manner describedsubsequently, thereby reversing the state of the flip-flop circuit fromthe Off to the On condition.

During transition, as the potential on control grid 26 drops below aparticular level, trigger tube 21 is cut off, anode current decreasesand anode potential rises toward a level of +10 volts. This transitionof anode potential of trigger tube 21 is coupled to control grid 25 oftrigger tube 22 through resistor 45 and capacitor 54, thereby raisingthe grid bias of trigger tube 22 to the conduction level, whereupontrigger tube 22 conducts and the potential on anode 24 drops toward alevel of -30 volts. The change in anode current through winding 35 oftransformer 37, arising from the positive variation in potential onanode 23, results in a negative potential being coupled to winding 36 oftransformer 37. This negative potential is applied directly to anode 24of trigger tube 22, thereby enabling the anode to reach a stable levelof -30 volts more rapidly. The negative potential is also appliedthrough resistor 48 and capacitor 52 to control grid as to assist inmaintaining trigger tube 21 in the cutoif state during transition. Aswill be shown and described in greater detail hereinafter, the resultsarising from the transformer coupling are reflected in the Waveform ofthe output signal on conductor 4 as a substantial decrease in rise timefrom the -30 to the +10 volt level. When the anode potential on triggertube 21 reaches the +10 volt level, it is clipped thereat by diode 60.Accordingly, the output signal on conductor 4 is at a level of +10volts. The anode potential of trigger tube 22 and the correspondingoutput level on conductor is maintained at a level of -30 volts byclipping diode 57 during the On condition of the flip-flop.

During the On condition of the flip-flop, trigger tube Zl isnon-conducting and its grid potential is considerably below cutoff.Control grid 26 is biased at approximately -22 volts with respect to thecathode, and a negative pulse, whether passed by diode 65 or not, doesnot affect the non-conducting state of this vacuum tube. Thus positivepulses applied to Set input terminal 2 during the On condition of theflip-flop have no effect.

The above described operation illustrates the transition of flip-flop 1from the Off to the On condition. The transition from the On to the Offcondition is accomplished in like manner.

A positive pulse applied to the Clear input terminal 3 results in anegative pulse being induced in secondary winding 72. The pulse passesthrough diode 73 and parasitic suppressor 53 to control grid 25 oftrigger tube 22. As trigger tube 22 is cut off, the corresponding anodecurrent decreases as the potential on anode 24 rises. This change ofcurrent is coupled through transformer winding 36 and appears on winding35 as a negative potential. This negative potential when applied throughresistor 45 and capacitor 54 to control grid 25 assists in maintainingtrigger tube cut ofi during transition. The negative potential is alsoapplied directly to anode 23 of trigger tube 21, enabling it'to fall toa stable level of -30 volts more rapidly. This operation is reflected inoutput conductor 4 as a drop in fall time from the to -30 volt level. Itis noted that rise and fall transformer coupling.

times on output conductor 4 correspond to fall and rise timesrespectively on output conductor 5. Diode and resistor 76 acrosstransformer winding 72 serve to limit positive overshoot voltages whichoccur on the upper side of secondary winding 72 of transformer 71 as theresult of the decay of the positive pulse applied through Clear inputterminal 3 to transformer primary winding 70. Upon completion of thetransition from the On to the Off condition, output conductors 4 and 5have potentials of -30 and +10 volts thereupon respectively.

From the above description it is apparent that two pulses are requiredto oausethe circuit to complete its cycle, i.e., for each tube to passfrom the non-conducting to the conducting state and vice versa. Witheach pulse applied to the circuit to reverse its conduction state, twoDC. level signals are generated, the DC. level of the tube beingtriggered being +10 volts and the DC. level of the opposite tube being-30 volts Summarizing the operation of the subject apparatus, to reversethe state of the flip-flop, a positive trigger pulse produces a negative0.1 ,usec. pulse in the transformer secondary winding and this negativepulse causes cutoff of the conducting tube. This produces a suddendecrease in the anode current and a corresponding rise in the anodepotential of the associated trigger tube. The rise of anode potential isapplied through a coupling network to reverse the conduction state ofthe formerly non-conducting tube to conduction. The variation in anodecurrent flow through a first winding of a 1:1 transformer produces anegative potential in the second winding of the transformer. Thisnegative potential is applied directly to the anode of the formerlynon-conducting tube to assist the anode in reaching its negative stablelevel more rapidly, and is applied through a coupling network to thecontrol grid of the cutoff tube to maintain cutoff during transition.Clipping circuits ensure uniformity of the DC. levels of the outputsignal.

Referring now to Fig. 2, curve a illustrates the negative pulses whichinitiate transition by terminating con- .duction of the normallyconducting tube, while curves 1) and 0 thereof illustrate the waveformof the output signal of the preferred embodiment with and without It isto be understood that the waveforms of Figures 2a through 2c do notrepresent actual quantitative values but represent in a general way thequalitative variations of the voltages with time. While it is recognizedthat some distortion is present in the illustrated waveforms, suchdistortion is not important to an understanding of the present inventionand accordingly has been omitted from the idealized waveforms of Fig. 2.

Curve b illustrates the general waveform of the output signal of thecircuit of Fig. 1 without transformer coupling at the anodes. Asheretofore described, the output signal has fixed lower and upper levelsprovided by clipping circuits of -30 and +10 volts respectively. Theoutput signal begins to rise from the -30 volts signal level shortlyafter the time when the negative pulse 83 begins to drop in the negativedirection. The duration of the output signal is determined by the timebetween trigger pulses. The waveform begins to fall shortly after pulse84 begins to fall. It should be noted that the slope of pulses 83 and 84is such that the pulses have a steep leading edge and are 0.1 usec. induration. The rise time of the waveform illustrated by curve b is thetime required for the anode of the cutoff trigger tube to travel fromits original level of -30 volts to a +10 volt level, while the fall timeis the time required for the same anode to revert from the +10 voltlevel to its original level of -30 volts.

Curve 0 of Fig. 2 illustrates the waveform of the output signal of thepreferred embodiment under the identical conditions described withreference to curve b except that transformer coupling is providedbetween the anodes of the trigger tubes. Curves b and c are operationmay be made by those skilled in the art with out departing from thespirit of the invention. It is the intention therefore, to be limitedonly as indicated by the scope of the following claims.

What is claimed is:

l. A trigger circuit including first and second electron tubes having atleast an anode, cathode and control grid, said tubes being adapted to bealternately rendered conductive to represent one or the other of twostable conditions means coupling the anode of said first tube to thecontrol grid of the second and the anode of said second tube to thecontrol grid of the first to permit transition from one to the otherstable condition, a transformer interconnected between each of saidcontrol grids and an input circuit for reversing the polarity of eachinput signal applied thereto, a further transformer having a primary andsecondary winding connected respectively to the anodes of said first andsecond tubes, said further transformer functioning to deliver thevoltage change resulting from termination of conduction in theconductive one of said tubes to the anode of the non-conductive tube andthereby enable the anode of the non-conductive tube to more rapidlyattain the potential level compatible with the other of said stableconditions, and output means connected to each of said anodes.

2. An electronic switching circuit comprising in combination first andsecond trigger tubes having opposite conduction states representing twostable conditions, means cross-coupling the anode of each trigger tubeto the control grid of the other whereby one of said trigger tubes isconducting and the other of said trigger tubes is non-conducting, saidanodes being further connected 6 to clipping means for providing stablepotential levels determined by the conduction state of the associatedtrigger tube, an input circuit associated with each of said triggertubes and adapted to reverse the potential of a signal applied thereto,a transformer having a primary Winding connected to the anode of saidfirst tube and a secondary winding connected to the anode of said secondtube and means for applying a signal to the input circuit associatedwith said conducting tube to terminate conduction thereof, saidtransformer responding to the resulting decrease in current flow in saidconducting trigger tube to cause a negative potential to be establishedon the anode of said non-conducting trigger tube more rapidly wherebythe transition speed of said electronic switching circuit issubstantially increased.

3. A bistable multivibrator circuit for generating out put signalshaving a frequency corresponding to the repetition rate of pulse signalsapplied thereto comprising in combination first and second vacuum tubeshaving at least an anode, a cathode and a control grid respectively,means cross coupling the anode of each vacuum tube to' the control gridof the other, input means connected to each of said control grids forapplying said pulse signals thereto to initiate transition of saidmultivibrator circuit and a transformer having a primary and secondarywinding connected to the anodes of said first and second vacuum tubes,said transformer being polarized to increase the transition speed ofsaid multivibrator circuit from one bistable state to the other uponapplication of a pulse signal to the appropriate control grid.

References Cited in the file of this patent UNITED STATES PATENTS WolfeJuly 7,

